In general the LMS 4.2 runs VRFcollection jobs and Summarizer jobs periodically. When you hit a high number of jobs (15K if I'm not wrong), you start to get an error message on Job browser page. Then the purging may come in handy.
Go to [Admin] > [Network] > [Purge Settings].
To purge the jobs related to VRF, see the topic "Purging VRF Management Reports Jobs and Archived Reports" on the following document.